With regard to the processing of poultry meat, the invention is based on the recognition that the processing of poultry produces low-quality meat, for example meat which has been mechanically removed from the bone and meat trimmings, which can be given a higher added value by being upgraded. Also, there is an increasing consumer demand for “moulded meat products”, for example for snacks, and for meat products with an attractive appearance. In these sectors, demand may change quickly, so that it must be possible to adapt the production method according to the invention quickly to meet demand. Furthermore, it is observed that the demand for moulded (meat) products is very high, and consequently it must be possible to achieve a high production capacity.
Various methods and moulding machines are known for moulding products from a (meat) mass, and a number of these methods and moulding machines will be described briefly below.
U.S. Pat. No. 4,987,643 has described a moulding machine of the “slide-plate” type, for the purpose of producing portions of hamburger meat. A machine of this nature has a substantially planar moulding plate containing a plurality of mould cavities for the meat mass. The moulding plate can be moved to and fro substantially in its horizontal plane for the purpose of displacing the mould cavities between a filling position, in which the mould cavities are filled with meat mass which has been placed under pressure by a meat pump, and a removal position, in which the moulded meat products are removed from the mould cavity. The capacity of a slide-plate machine of this nature is limited in particular by the rate at which the mould plate can be moved to and fro; it is necessary for the mould plate of the known machine to come to a standstill at the filling and removal positions. The speed of movement of the mould plate is limited by the inertia forces which are generated by the heavy mould plate which is moving to and fro and the components which are connected thereto. The reciprocating movement is partly limited by the fact that the mass which is introduced into the mould cavity under a filling pressure has to remain in the closed mould cavity for a certain period in order to obtain the desired cohesion or adhesion of the pieces of meat. The design of these known moulding machines of the slide-plate type has proven unsuitable or, at any rate, disadvantageous for further increasing the production capacity, which would be desirable in view of the increasing demand for moulded meat products.
Another known type of moulding machine for meat products and the like is the “turret-type”, an example of which is described in U.S. Pat. No. 4,193,167. In this type of moulding machine, the mould cavities are arranged on a horizontal rotating wheel which can be rotated about a vertical axle. The mould cavities have an opening on the underside of the rotary wheel, so that the mould cavities extend parallel to the axis of rotation of the rotary wheel. Opposite the opening of the mould cavity, this known moulding machine has a mechanically displaceable base, the movement of the base being derived, via a cam-disc mechanism, from the rotation of the rotary wheel. The operation of the associated filling device is synchronized with respect to the rotation of the rotary wheel. In this known moulding machine, the large number of and interaction between the moving components again limits the extent to which the capacity can be increased. Particularly when removing the moulded products, the adhesion of the meat mass to the side wall and the base of the mould cavity represents a problem for operating with success at high speed. The way in which the mould cavities are filled in this known machine also limits the production capacity.
Another type of moulding machine for moulding three-dimensional products from a meat mass or the like is the “rotating drum type”. Known moulding machines of this type have a rotatable drum which is driven in continuous rotation by an associated drive, with a plurality of mould cavities on the outside of the drum, which cavities, in a filling position, move past a filling component which is arranged along the outside of the drum and by means of which the mould cavities are filled with (meat) mass. In a removal position, which is located further on in the direction of rotation of the drum, the moulded meat products are driven out of the mould cavities. In this type of machine, the mould cavities are located transversely with respect to the axis of rotation of the drum.
Examples of known moulding machines of the “rotating drum type” are described in U.S. Pat. No. 3,504,639, U.S. Pat. No. 3,851,355, U.S. Pat. No. 4,212,609, GB 2,259,043, FR 2,491,734 and FR 2,538223. The development of the moulding machine of this “rotating drum type” is currently not sufficiently advanced for achieving the production capacity required both currently and in the future, and consequently the abovementioned slide-plate moulding machines have the highest capacity and are used for mass production.
In the following text, it is assumed that a filling pressure is exerted on the (meat) mass which is to be introduced into the mould cavity in order to fill the mould cavity with a portion of the mass. Therefore, the filling pressure is the pressure which is exerted on the (meat) mass while the mould cavity is being filled.
In order to ensure that the (meat) pieces of which the mass consists adhere to one another, thus producing a dimensionally stable product, after the mould cavity has been filled with the (meat) mass, the mass has to be subjected to a fixing pressure for a fixing period which takes place at some point between the time at which the mould cavity is filled and the time at which the moulded product is removed and during which period the portion of the mass is enclosed in the mould cavity. After the fixing period, an edible product which forms a cohesive unit in a three-dimensional shape is obtained, which product can then be removed from the mould cavity.
In known moulding machines, such as for example the moulding machine which is described in EP 0,447,003, a portion of the mass is pressed into the open mould cavity by the filling component under a filling pressure. Then, the mould cavity is closed by the fact that the moulding plate with its mould-cavity opening slides away from under the opening of the filling component and moves under a closed top plate. Inevitable leakage from the mould cavity and/or relaxation of the mass in the mould cavity indicates that the pressure of the mass in the mould cavity falls slightly after the cavity has been closed. In the context of the present application, the pressure which then prevails in the closed mould cavity is regarded as being the fixing pressure. This fixing pressure remains present during the displacement of the mould plate until the mould cavity reaches the opening in the bottom plate, with the result that the mould cavity is opened to atmosphere. In this known moulding machine, the fixing pressure is therefore directly and exclusively related to the filling pressure, and it is impossible to control the fixing pressure independently of the filling pressure. Also, the duration of the filling period and the fixing period cannot be influenced independently of one another, since they are both determined by the displacement speed of the moulding plate of the moulding machine. A final drawback is that as soon as the opening in the bottom plate is reached, the mass in the mould cavity, which is still under pressure, immediately seeks to escape from the opening which is increasing in size, and this has an adverse effect on the shape of the product.